Motion lab · chemical reactions

Reaction Heat and pH Lab

Test the pH with pH paper, then mix the reactants and watch the thermometer. Does each reaction give off heat or take it in?

Steps

    Options

    Speed

    Controls:
    Thermometer Drag it into the beaker.
    pH paper Drag a strip into a liquid.
    Stopwatch 00:00.00
    pH color chart

    Your test strips

    How to use this simulation
    1. Pick Part 1 or Part 2 under Reaction. Follow the Steps list. Each step gets a check mark when you finish it.
    2. To test pH, drag a strip from the pH paper card into a liquid. The strip changes color. Open the pH paper tab and match each strip to the pH color chart. Write down the color and the pH.
    3. Drag the Thermometer into the beaker. Its card shows the Start temperature and the temperature Now.
    4. In Part 2, the vinegar sits in a hot water bath. Wait until it reads 32 to 38 °C, then press Take it out of the water bath.
    5. Press Play (the triangle) to pour the yeast or baking soda into the beaker. The Stopwatch starts by itself. You can also start, stop and reset it.
    6. Read the temperature every 15 seconds for 2.5 minutes. The Table tab saves every reading too, and the Graph tab draws them.
    7. Press Pause to freeze time. Press Reset to run the part again. Choose 5 times faster if you are in a hurry.
    Exothermic and endothermic

    A chemical change makes new substances. One sign of a chemical change is a change in energy, like heat or light.

    An exothermic reaction releases energy as heat. The mixture and the thermometer get warmer.

    An endothermic reaction absorbs energy as heat. It pulls heat from its surroundings, so the mixture gets colder.

    In an exothermic reaction, the products end up with less energy than the reactants, because energy left as heat. In an endothermic reaction, the products end up with more energy than the reactants, because energy was taken in.

    Most reactions are fastest right after the reactants mix, so the temperature changes the most at the start. Later the reaction slows down, and the temperature changes less.

    pH and pH paper

    pH measures how acidic or basic a substance is. The scale goes from 0 to 14.

    A pH below 7 is an acid. The lower the number, the stronger the acid. A pH of 7 is neutral, like pure water. A pH above 7 is a base.

    pH paper has chemicals in it that change color. Dip a strip in a liquid, then compare its color to the chart. The closest color tells you the pH.

    The chemistry
    • Part 1: 2H2O2 → 2H2O + O2. Yeast has catalase, a protein that speeds up this reaction. The bubbles are oxygen gas.
    • Part 2: NaHCO3 + CH3COOH → CH3COONa + H2O + CO2. Baking soda reacts with the acid in vinegar. The bubbles are carbon dioxide gas.
    • The vinegar is warmed first so it has heat to give. That makes the cooling easier to see.